1. Field of the Invention
The present invention relates to a pneumatic tire having at the tread thereof blocks in which sipes are formed, and in particular, to a pneumatic tire in which irregular wear is suppressed and noise at the time of wear is decreased.
2. Description of the Related Art
Generally, in pneumatic tires provided with block patterns, irregular wear known as heel-and-toe wear, results in steps due to wear at the leading (step-in) edges and the trailing (kick-out) edges of blocks, and tends to occur. Such wear is accompanied by a deterioration in external appearance and noise, and there is a definite need to solve this drawback.
With heel-and-toe wear a step is formed due to earlier wear at the toe side which is the trailing edge, than at the heel side which is the leading edge.
An example of a method for improving heel-and-toe wear is a method in which the angle of the groove wall surfaces with respect to a normal line which is orthogonal to the direction in which the groove extends, is changed at the leading edge and the trailing edge.
However, it is difficult to greatly change the angle of the groove wall surfaces due to problems such as removing the tire from a mold at the time of vulcanization or the like. Further, as wear progresses, the width of the groove has a distribution which differs greatly than that at the time the tire was new, which is not preferable from the standpoint of performance nor from the standpoint of external appearance
Further, as can be seen from Japanese Patent Application Laid-Open (JP-A) No. 2-24204, an idea has been proposed in which sipes are disposed parallel to the contour line at the leading edge of the ground-contact configuration. However, this structure can only be applied to patterns having a specific orientation, and is not practical.